Underground cable systems including power (energy) cables or data communications and telecommunications cables are invariably susceptible to damage and degradation caused by infiltration and migration of water into cable cores. Water is particularly hazardous to fiber optic cable, causing long-term reduction in transmission reliability and outright transmission failure.
Fiber optic cables are susceptible to water damage due to, for instance, mechanical damage to an outer cable jacket or a sheathing system that allows water to penetrate into a central core or buffer tubes containing optical fibers. Exposure of optical fibers to water causes microbending wherein water near or surrounding the optical fibers freezes and stresses the structure of the optical fibers, causing optical fibers to bend. Microbending degrades optical fibers and increases losses of signal transmission. Changes in ambient conditions also expose optical fibers to moisture. Such changes create different vapor pressures inside and outside a cable jacket that cause moisture to diffuse through the jacket into a central core or group of buffer tubes, exposing the optical fibers to undesirable moisture.
Many cable products are provided with one or more forms of water blocking 25 protections to prevent ingress and migration of water. Prior art water blocking protections are incorporated with cables in various forms including waterproof jackets, water blocking layers incorporated between a central core and a core or jacket, water blocking yarns, water blocking tapes, and combinations thereof. Such water blocking protections impart water blocking capabilities to underground cable to prevent water penetration through cable sheathing systems toward central core areas, e.g., containing optical fibers, and to prevent further damage caused by water migration along cable axes. Prior art water blocking tapes are often disposed between a central core and a sheathing system or outer cable jacket. For instance, U.S. Pat. No. 6,173,100 discloses a water blocking tape disposed between a core and an outer jacket. The tape includes two or more layers of material with fibers. The fibers form a matrix for bonding with and retaining superabsorbent polymers applied to the layers. U.S. Pat. No. 5,642,452 discloses a fiber optic cable including a water blocking system comprising a protective layer with water swellable characteristics disposed between a core and a jacket. The cable also includes one or more water blocking yarns with swellable characteristics that extend longitudinally along the cable. The blocking yarns and the protective layer are treated with a superabsorbent compound, such as polyacrylic acid, to impart swelling characteristics to the yarns and the protective layer before incorporation with the cable.
Other prior art water blocking protections include strength members treated with water absorbing compounds. U.S. Pat. No. 5,163,115 discloses a water blocking member treated with a saline-tolerant, temperature-resistive superabsorbent polymer. European Publication No. 0 314 991 Bi discloses a substrate member disposed between an inner central core containing optical fibers and a plastic cable jacket that is impregnated with a film or a paste of a water swelling or superabsorbent material, such as polyacrylic acid or polyacrylamide. European Publication No. 0 827 625 Bi discloses a water blocking composite impregnated with or having a coating of a mixture of a radiation polymerized 20 compound and a water swellable compound.
Layered water blocking tapes are, however, susceptible to “fall-out” or loss of water blocking compounds contained between layers of material during cable manufacture. For certain applications, water blocking tapes and materials must be sufficiently thin and flexible for use, for instance, with certain cable designs, such as fiber 25 optic cable. Such tape configurations can limit the amount of water absorbent compounds that may be loaded between layers of material. Multilayer water blocking tapes are often sealed or bonded with adhesives and bonding agents, and, in some cases, are necessary for containment of water blocking compounds. Such adhesives and bonding agents can inhibit the swelling action of water blocking compounds when contacted by water and can limit the extent to which water blocking tapes may swell and increase in thickness, compromising the tapes water protection properties.
Thus, a water blocking tape is desirable that can overcome at least some limitations of multilayer tapes. In addition, a water blocking tape configured to contain one or more water absorbent compounds sufficient to provide a required swell height is desirable. A water blocking tape is also desirable that provides a substantially consistent distribution of one or more water absorbent compounds between layers to ensure consistent swell height. Forming a water blocking tape without use of adhesives and/or bonding agents is also desirable to help to maximize the tape's swelling action and swell height. A water blocking tape that is lightweight and has sufficient flexibility for use with certain cable designs, such as fiber optic cable, is desirable.